Apparatuses for measuring communication quality of a network and node apparatuses for taking traffic control based on a result of the measurement are sometimes provided therein with a table for managing statistic information on communication quality, based on which processing of traffic control thereafter is determined.
A conventional technique of this type is disclosed in Non-patent Document 1, for example.
NetFlow disclosed in Non-patent Document 1 (RFC3954 of Internet Engineering Task Force) describes a technique for creating statistic information in a node apparatus to measure quality of a network. Specifically, NetFlow is a mechanism provided in a router or a measuring probe for measuring quality of a network, and has the following functions (1), (2), (3):
(1) a function of capturing some or all of packets passing through an interface of a router;
(2) a function of updating statistic information present in the router from the captured packets; and
(3) a function of creating packets at regular periods from a result of the statistic information in conformity with the format of NetFlow stipulated by RFC3954 or the like, and sending them to a data analysis apparatus.
By these functions, the data analysis apparatus collects information for packets passing through a router having the NetFlow mechanism to monitor quality of a network (mainly, the amount of traffic). For the function (2), a table provided in the data analysis apparatus is used to record statistic information such that one entry contains one flow, and update the statistic information. Since the number of entries is limited, the entry information should be swapped in turn in order to operate the apparatus over a long period of time. Methods therefor generally include: an inactive timer for deleting an entry of flow when communication having information representing the flow is not encountered over a certain period of time; an active timer for sending entry information to a data analysis apparatus or deleting it at regular periods even when communication continues; a method of deleting an entry when communication is completed by checking flag information such as “FIN” or “RST” of TCP (Transmission Control Protocol); an FIFO (First In First Out) scheme in which an entry registered earlier is precedently deleted when a cache becomes full; and an LIFO (Last In First Out) scheme in which an entry registered latest is precedently deleted, although depending upon the application.
A network quality control technique disclosed in Non-patent Document 2 is a technique for an apparatus for creating statistic information in the apparatus and taking traffic control based on a result thereof.
Specifically, the apparatus is for traffic transfer/control such as, for example, a router, and has the following functions (1), (2), (3), (4):
(1) determining an output route for an input packet;
(2) updating statistic information present in the apparatus based on the input packet;
(3) determining discardability of the input packet based on the statistic information; and
(4) processing the packet based on results of (1) and (3) (either transferring the packet to the output route or discarding the packet).
This apparatus is provided with a table for recording therein statistic information such that one entry contains one flow; however, since an enormous amount of entries would be required when statistic information for all flows are managed, packet sampling is applied to reduce the amount of packets to be observed, and statistic information for flows are created based on the reduced amount of packets.    Non-patent Document 1: B. Claise, “Cisco Systems NetFlow Services Export Version 9,” IETF, RFC3954, October 2004.    Non-patent Document 2: Rie HAYASHI, Takashi MIYAMURA, Kohei SHIOMOTO, Shigeo URUSHIDANI, “Network QoS control mechanism by real-time measurement of elephant flows,” IEICE Technical Report (NS2005-117, CQ2005-71, TM2005-11), November 2005.